Re: [PATCH 1/8] fwctl: Add basic structure for a class subsystem with a cdev

Jonathan Cameron
2024-06-05T11:08:41Z

On Tue, 4 Jun 2024 15:52:00 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Tue, Jun 04, 2024 at 06:05:55PM +0100, Jonathan Cameron wrote:
>
> > Trick for this is often to define a small function that allocates both the
> > ida and the device. With in that micro function handle the one error path
> > or if you only have two things to do, you can use __free() for the allocation.
>
> This style is already followed here, the _alloc_device() is the
> function that does everything before starting reference counting (IMHO
> it is the best pattern to use). If we move the ida allocation to that
> function then the if inside release is not needed.
>
> Like this:

LGTM (this specific code, not commenting on fwctl in general yet as needs
more thinking time!)

>
> diff --git a/drivers/fwctl/main.c b/drivers/fwctl/main.c
> index d25b5eb3aee73c..a26697326e6ced 100644
> --- a/drivers/fwctl/main.c
> +++ b/drivers/fwctl/main.c
> @@ -267,8 +267,7 @@ static void fwctl_device_release(struct device *device)
> struct fwctl_device *fwctl =
> container_of(device, struct fwctl_device, dev);
>
> - if (fwctl->dev.devt)
> - ida_free(&fwctl_ida, fwctl->dev.devt - fwctl_dev);
> + ida_free(&fwctl_ida, fwctl->dev.devt - fwctl_dev);
> mutex_destroy(&fwctl->uctx_list_lock);
> kfree(fwctl);
> }
> @@ -288,6 +287,7 @@ static struct fwctl_device *
> _alloc_device(struct device *parent, const struct fwctl_ops *ops, size_t size)
> {
> struct fwctl_device *fwctl __free(kfree) = kzalloc(size, GFP_KERNEL);
> + int devnum;
>
> if (!fwctl)
> return NULL;
> @@ -296,6 +296,12 @@ _alloc_device(struct device *parent, const struct fwctl_ops *ops, size_t size)
> init_rwsem(&fwctl->registration_lock);
> mutex_init(&fwctl->uctx_list_lock);
> INIT_LIST_HEAD(&fwctl->uctx_list);
> +
> + devnum = ida_alloc_max(&fwctl_ida, FWCTL_MAX_DEVICES - 1, GFP_KERNEL);
> + if (devnum < 0)
> + return NULL;
> + fwctl->dev.devt = fwctl_dev + devnum;
> +
> device_initialize(&fwctl->dev);
> return_ptr(fwctl);
> }
> @@ -307,16 +313,10 @@ struct fwctl_device *_fwctl_alloc_device(struct device *parent,
> {
> struct fwctl_device *fwctl __free(fwctl) =
> _alloc_device(parent, ops, size);
> - int devnum;
>
> if (!fwctl)
> return NULL;
>
> - devnum = ida_alloc_max(&fwctl_ida, FWCTL_MAX_DEVICES - 1, GFP_KERNEL);
> - if (devnum < 0)
> - return NULL;
> - fwctl->dev.devt = fwctl_dev + devnum;
> -
> cdev_init(&fwctl->cdev, &fwctl_fops);
> fwctl->cdev.owner = THIS_MODULE;
>
> Jason